Light-transmitting optical components, such as prisms, windows, and lenses, are frequently used in optical systems for a laser or other light source. The effect of a light-transmitting optical component on the emergent wavefront represents an important specification for the optical component. Light absorption by the optical component develops internal thermal gradients which are manifested as wavefront distortions. A wavefront distortion is the total, peak-to-peak, deformation in the direction of propagation of the emergent wavefront from its intended shape. Wavefront distortions can cause spherical lensing or other distortions that degrade the overall performance of the optical system.
Accordingly, it is generally desirable to measure the light absorption of optical components to assess their performance prior to being incorporated in an optical system. Measuring optical absorption indirectly by using optical detectors such as photodiodes or photomultipliers represents one well known method of measuring the absorption of optical components. In particular, this method involves comparing the difference between the intensity of a light beam entering an optical component and the intensity of the light beam exiting the optical component (and accounting for reflection losses which also must be measured) to calculate the absorption of the optical component.
Unfortunately, measurements performed by the above-described method become increasingly difficult as the absolute value of the absorption of the optical component decreases. For example, absorptions may be on the order of 1% or less of the incident light. The above-described method is especially difficult when differences on the order of a fraction of a percent are important, because drift and noise in the optical source and the optical detectors limit the accuracy of the absorption measurements. Further, this method requires deducing the absorption by measuring the difference between two potentially very large numbers (i.e., the intensity of a light beam entering the optical component and the intensity of the light beam exiting the optical component). Moreover, this method requires several expensive optical sensors which must be placed in a spread-out arrangement for each optical component to be tested.
What is needed is a better structure and technique for measuring optical absorption so that light-transmitting optical components are selected efficiently and accurately for use in a particular optical system.